Mass spectrometry (MS) is an analytical technique that can be used to determine the chemical composition of a sample, and to supply data important to assigning the chemical structures of the components. It does so by ionizing the components to generate charged molecules and molecule fragments, and then measuring their mass-to-charge ratios. In an MS procedure, a sample is introduced into the MS instrument, typically by a pump or syringe, and its components undergo ionization through one of a variety of mechanisms resulting in the formation of charged particles. The mass-to-charge ratio of the particles can then be calculated based on behavior of the ions as they pass through electric and magnetic fields generated by the MS instrument.
Electrospray ionization (ESI) is one technique used in MS to produce ions. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. In electrospray ionization, a liquid is pushed through a very small, charged and usually metal, capillary. This liquid contains the substance to be studied, the analyte, dissolved in a large amount of solvent, which is usually much more volatile than the analyte. Volatile acids, bases or buffers are often added to this solution too. The analyte exists as an ion in solution either in its anion or cation form. Because like charges repel, the liquid pushes itself out of the capillary and forms an aerosol. An uncharged carrier gas such as nitrogen is sometimes used to help nebulize the liquid and to help evaporate the neutral solvent in the droplets. As the solvent evaporates, the analyte molecules are forced closer together, repel each other and break up the droplets. This process is called Coulombic fission because it is driven by repulsive Coulombic forces between charged molecules. The process repeats until the analyte is free of solvent and is a lone ion.
As MS usage and applications continue to increase, there continues to be a need for improved MS systems and improved components for use in MS systems and methods.